Effect of Foundation-Reservoir Interaction on Seismic Behaviour of Gravity Dams

This paper discusses the combined effect of foundation-reservoir interaction on the seismic response of concrete gravity dam by considering a case study: Bichom Concrete Gravity Dam located in Arunachal Pradesh, India. The dam comprises of overflow and non-overflow monoliths and seismic analysis was carried out for both monoliths separately for Design Basis Earthquake excitation (DBE) assuming linear behaviour. The significance of foundation flexibility on the seismic response of dam was investigated by comparing the response of dam with rigid and flexible foundations. The hydrodynamic effect of impounded water is modeled as an added mass by Chopra’s Method. Effect of foundation-reservoir interaction on the response of both monoliths, such as time period, crest displacement, base reactions and stress distributions are discussed in this paper. It is predicted from the analysis that the dam with rigid foundation is relatively safe except some minor cracks at the heel of non-overflow monolith, but the dam with flexible foundation suffers moderate damage when the reservoir is empty and full

Measurement and Analysis of Horizontal Vibration Response of Pile Foundations

Pile foundations are frequently used in very loose and weak deposits, in particular soft marine clays deposits to support various industrial structures, power plants, petrochemical complexes, compressor stations and residential multi-storeyed buildings. Under these circumstances, piles are predominantly subjected to horizontal dynamic loads and the pile response to horizontal vibration is very critical due to its low stiffness. Though many analytical methods have been developed to estimate the horizontal vibration response, but they are not well validated with the experimental studies. This paper presents the results of horizontal vibration tests carried out on model aluminium single piles embedded in a simulated Elastic Half Space filled with clay. The influence of various soil and pile parameters such as pile length, modulus of clay, magnitude of dynamic load and frequency of excitation on the horizontal vibration response of single piles was examined. Measurement of various response quantities, such as the load transferred to the pile, pile head displacement and the strain variation along the pile length were done using a Data Acquisition System. It is found that the pile length, modulus of clay and dynamic load, significantly influences the natural frequency and peak amplitude of the soil-pile system. The maximum bending moment occurs at the fundamental frequency of the soil-pile system. The maximum bending moment of long piles is about 2 to 4 times higher than that of short piles and it increases drastically with the increase in the shear modulus of clay for both short and long piles. The active or effective pile length is found to be increasing under dynamic load and empirical equations are proposed to estimate the active pile length under dynamic loads